Removal of organic solvents from aqueous process streams comprising the same is required in particular in recovery of metals by leaching wherein electrolyte solutions resulting from leaching of metal containing starting materials, such as ores and concentrates, are purifier prior to further processing stages such as electrowinning.
Typically removal of the organic solvents is accomplished by passing the aqueous process streams comprising organic solvents through a filter comprising anthracite particles. Upon contact with the anthracite particles in the filter the organics form small droplets in the liquid joining together forming lager droplets. At a certain droplet size the buoyance force will lift the droplet off the anthracite surface and the droplet moves up to the surface of the liquid where a layer of organics is collected.
One of the problems associated with the use of anthracite particles for separating the organics from the aqueous process stream is that for ensuring good organics removal the flux through the anthracite bed should be low enough to give enough residence time for the coalescence to take place. Typically the cross sectional flux i.e. the cross section filtration velocity in the filter is approx. 12 m/h. This means that fairly large amounts of anthracite must be used to get good filtration.
A further problem is that anthracite can be used for only about one year if regenerated properly with back-flush with water and/or air bubbles. Upon cleaning the anthracite is subjected to mechanical wear and the anthracite particles tend to get damaged. After this the anthracite must be treated as hazard waste that has to be destroyed as regeneration for reuse is not possible.